Multiple immunological parameters, including total lymphocyte count, lymphocyte subpopulations (CD2+, CD19+, CD3+, CD4' and CD8+), phytohemagglutinin (PHA) response, and natural killer (NK) activity, were measured in 66 patients with previously untreated esophageal carcinoma. The influence of preoperative treatment and/or surgical operation on the immune function were evaluated in 40 patients. The PHA response and NK activity of the patients with esophageal carcinoma were 229 k 103 S.I.% and 18.5 2 11.9% lysis, respectively, and were significantly depressed as compared with the control. The CD4+1CD8' ratio, PHA response, and NK activity in stage IV were also significantly depressed compared to that in stages 1-111. Preoperative treatment induced significant reductions in the total lymphocyte count (1,994 & 644 to 670 +-274/mm3), PHA response (219 t 77 to 159 k 59 S.I.%), and NK activity (19.7 k 13.2 to 11.1 * 10.3% lysis) as well as a significant gradual decrease in the CD4+/CD8+ ratio (2.09 ? 1.42 to 0.69 k0.48), while the surgical operation significantly influenced only the total lymphocyte count. This study demonstrates that preoperative treatment induces a more pronounced influence on the immune function than surgical operation alone, in patients with esophageal carcinoma in which the immune function is disturbed prior to these treatments.